This invention relates to interior space daylighting systems and, in particular, to a mini-optical light shelf daylighting system that implements an efficient daylighting system to redirect incident daylight on to the ceiling plane of an interior space to illuminate the interior space.
It is a problem in the field of interior space illumination to provide a cost effective mode of illumination that makes use of the incident daylight without the need for complex systems or significant occupant intervention. Existing daylighting systems are of limited effectiveness, limited applicability due to their architectural limitations, or require complex and expensive mechanical and electronic control mechanisms.
Each year in the United States, over $350 billion is spent on energy for residential, commercial, and industrial buildings. Of this amount, more than $212 billion was spent during 1996 to purchase electricity, with 32% of that amount being used to operate commercial buildings: office, retail, institutional, but not industrial. Of this use, approximately 35% of the electricity consumption was related to lighting and another 6% was attributable to the air conditioning energy required to remove the excess heat generated by electric lighting. Thus, lighting is typically the largest end-use for electricity, annually consuming approximately 310 billion kWh.
There is a need for systems that provide improved energy efficiency and environmental quality in buildings. One such example is a system that reduces the consumption of electricity for lighting. One option for reducing electricity consumption for lighting is to use daylight to illuminate occupied building spaces during daylight hours. These systems are termed xe2x80x9cdaylighting systems.xe2x80x9d The key to the widespread use of daylighting systems is the provision of such a system that is both inexpensive and easily applied to both new and existing buildings. In addition to the savings attributed to reduced electricity consumption, daylighting systems typically also result in increased productivity by the occupants of the illuminated space, reduced health problems evidenced by the occupants of the illuminated space and pollution reduction. This is because there appears to be a strong correlation between the quality of the luminous environment and exposure to daylight and the overall health and productivity of the occupants. These ancillary benefits can produce savings that dwarf the savings attributable to electricity consumption reduction, since studies indicate that, over the life of the building, approximately 97% of the operating cost of commercial space is the salaries of the occupants and any improvement in the performance of the occupants of the building space results in a significant economic benefit.
One such existing daylighting system is the traditional interior light shelf, which comprises an optical device which receives daylight that is transmitted through a window and redirects it onto the interior ceiling plane, thereby creating a useful source of interior illumination. The basic light shelf concept typically comprises a wide flat elongated interior light shelf located adjacent to a window and protruding into a room from the exterior wall of a building, and/or an exterior light shelf of weather-resistant construction projecting from the exterior wall of the building, coplanar with the interior light shelf to receive incident daylight. The incident daylight is reflected by the interior and/or exterior light shelves onto the ceiling of the occupied space by a diffuse or specular horizontal or slightly sloped surface of the light shelf, which light reflecting surface is located above a view glazing. However, the interior light shelf typically protrudes a significant distance into the occupied space and is problematic from architectural, mechanical and aesthetic standpoints in many room applications.
Thus, the field of interior space illumination systems is devoid of an inexpensive, practical, effective and simple to use daylighting system that can be easily implemented in both existing building applications as well as in new building construction.
The above-described problems are solved and a technical advance achieved in the field by the present mini-optical light shelf daylighting system. The mini-optical light shelf daylighting system is implemented in the paradigm of a window treatment that is applicable to both new installations as well as existing window glazing. In particular, the mini-optical light shelf daylighting system is a passive, static optical device that is typically mounted juxtaposed to a window opening of a building above head height. The mini-optical light shelf daylighting system receives daylight transmitted through the window and efficiently redirects it uniformly onto the interior ceiling plane of a room (or other interior space) in a diffuse manner, thereby creating a useful source of interior illumination.
The mini-optical light shelf daylighting system comprises multiple optical shelves, each of which allows light to be efficiently collected and accurately directed onto the ceiling plane of a room, while at the same time shading the occupants of the room from direct daylight penetration above 15xc2x0 through the optical shelves. The optical shelves are narrow and can be implemented in the paradigm of a mini-blind window treatment. The window area is typically partitioned into a view related glazing section and a daylight collection and redirection glazing section. The occupant""s views out of the building remain unobstructed through the view related section of the glazing to a height of approximately seven feet above the floor. Traditional window treatments can be used for this portion of the glazing for shading, privacy, and blackout control. The daylight incident on the daylight collection section of the glazing is collected by the optically shaped top surface of the optical shelves of the mini-optical light shelf daylighting system and redirected onto the ceiling plane of the room in a glare free, uniform manner.
The mini-optical light shelf daylighting system produces effective daylighting for typical ambient light levels for the perimeter zones of a building, and can operate for room depths in excess of 35 feet deep, depending on the particular implementation of the mini-optical light shelf daylighting system. The optical geometries of the optical shelves and the associated reflective surface characteristics cooperatively diffuse the collected daylight uniformly across the ceiling plane of the room. The resultant indirect lighting is striation free and substantially uniform in illuminance. The use of daylight preserves the visual and psychological connection between the occupants and the outdoors due to the subtle color and illuminance changes which occur throughout the day. Visual comfort is enhanced by evenly diffusing the daylight across the ceiling plane of the room from the perimeter wall to the interior extent of the illumination.